Final answer:
The most popular access control list model used in file sharing is the Discretionary Access Control (DAC), which allows resource owners to set access permissions.
Step-by-step explanation:
The most popular access control list (ACL) model used in file sharing is the Discretionary Access Control (DAC).
In the context of file systems, an ACL is a list that tells which users or system processes are granted access to objects, as well as what operations are allowed on given objects. Each entry in a typical ACL specifies a subject and an operation. For example, if a file has an ACL that contains (Alice: read, write; Bob: read), this would give Alice permission to read and write the file and Bob to only read it.
DAC is a type of access control system that allows the owner of the resource to set the policies on who is allowed to access it. The owner can give read and write permissions to others at their discretion, making it a flexible system that is widely used in many operating systems and file-sharing environments.